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00:30Hello, thank you, and welcome once again to Think of a Numbar.
00:33And this time, it's all about time.
00:35So watch, watch, watch, watch.
00:41I dropped this watch the other day. It didn't break. It landed on its hands.
00:45This programme is all about time.
00:48We'll be discussing what makes the world go round.
00:50We'll be looking at swings in a roundabout sort of way.
00:53We'll be looking at time from the days when it went drip, drip,
00:56to when it went tick-tock, to today when it goes pulse-pulse.
01:00And we'll be considering how it's possible to split a second 9 billion times.
01:07But first of all, I'm going to ask a calendar question.
01:10Does anybody know how many months I've got 30 days?
01:14Anybody?
01:14Four, three, no, 11, you see.
01:19In fact, they've all got 30 days except February.
01:22But some of them have also got 31 days.
01:25And this is a page from a calendar.
01:29It's a wall calendar, but it's too big, so we put it on the floor.
01:31And it could be any month.
01:33On the 5th of the month, my doctor told me to take some medicine for seven days running.
01:38And then skip a week.
01:42The reason we've got this is we thought that you'd like to look at it.
01:46Now, there's several ways to look at a calendar.
01:47You can look at it and then forget it.
01:49Or you could perhaps look at each square one second at a time.
01:54And if you did that, you'd take 31 seconds to look at the calendar.
01:59But here's another way you might look at it.
02:02If you looked at this square for one second,
02:04and then this square for two seconds,
02:05and then this square for four seconds,
02:08and this one for eight seconds,
02:10doubling up all the time,
02:12how long do you think it would take you to look at the whole calendar,
02:16the 31 squares?
02:17How long? Anybody know?
02:1862 seconds.
02:2062 seconds?
02:21No, I don't think you've got the principle right.
02:23It's actually longer than that.
02:25Let's try it and see how long it takes.
02:27We'll look at this one for one second,
02:29this one for two seconds,
02:31so this one we'll look for four seconds,
02:34and then eight seconds.
02:37This one we'd look at for 16 seconds,
02:4032 seconds,
02:4364 seconds.
02:44Well, 64 seconds is just over a minute
02:46we'd spend looking at this one square.
02:49The next square, two minutes,
02:50four minutes,
02:52eight minutes,
02:5316 minutes,
02:54and then the 12th,
02:56we'd spend
02:5732 minutes looking at this one square,
03:01which is over half an hour.
03:02It's longer than this programme.
03:03And I think I'd rather watch any television programme
03:05rather than just look at one square for half an hour.
03:08However,
03:09the next square,
03:09we'd spend just over an hour looking at it.
03:11Then two hours,
03:13four hours,
03:14eight hours,
03:1616 hours,
03:1632 hours,
03:19we'd spend just looking at this square,
03:20which is
03:21practically a day and a half.
03:24So here,
03:25we'd spend
03:25three days
03:27just looking at this square.
03:28Then six days,
03:30that's without going to bed,
03:32you know,
03:32then 12 days,
03:3324 days,
03:3548 days,
03:36by the time we got to the 26th,
03:38we'd spend
03:38just over a year
03:40looking at this one square.
03:41And then
03:43two years,
03:44four years,
03:46eight years,
03:4716 years.
03:50And on the 31st,
03:51we'd spend
03:52actually
03:5233 and a half years
03:55looking at this one square.
03:57But we'd already have spent
03:5833 and a half years
04:00looking at all the other squares.
04:02So altogether,
04:03you'd have to spend
04:0467 years
04:06to look at just one page of the calendar.
04:1067 years?
04:11It's a lifetime.
04:13And you can't waste
04:14a life
04:15just looking at one page of the calendar.
04:17You can't waste time.
04:18See, time does not stop.
04:20It keeps going
04:21at a regular pace.
04:23And time
04:23is regulated
04:24by the Earth's movement
04:25round the sun
04:26and the Earth's movement
04:27round its own axis.
04:30Have a look.
04:32This is a model
04:34of the Earth
04:35and it spins
04:36in this direction.
04:41and the sun
04:44constantly shines on it
04:46and turns every 24 hours
04:48into night time
04:50and daytime.
04:57Now,
04:59around the Earth
05:00we've marked a line,
05:01a white line.
05:01It's not really there
05:02on the Earth.
05:04I used to have a friend
05:04who painted white lines
05:05in the road.
05:06He went round the bend.
05:09This is an imaginary line
05:10that runs round the centre
05:11of the Earth
05:11and it's called the equator
05:12and it's 25,000 miles long
05:14or thereabouts.
05:16Now,
05:16if the Earth revolves
05:17once every 24 hours,
05:19that means anyone
05:20standing
05:20on this line
05:21must be travelling
05:23all the time
05:24at just over
05:251,000 miles an hour.
05:26Now,
05:28where do we live?
05:30Here we are.
05:31Stop the Earth.
05:32There.
05:33We live up here
05:34and where we live
05:35it's not as far
05:36round the Earth
05:37but we
05:38and the Earth
05:39we're standing on
05:40is at this moment
05:41travelling
05:42at around
05:43600 miles an hour.
05:46But that's
05:47300 yards
05:48every second
05:49which means
05:50if I jump up
05:51in the air
05:51for half a second
05:52I should come down
05:53150 yards
05:54over there.
05:55So let's try it.
05:571, 2, 3
05:58Jump!
06:00Where's he gone?
06:01What's happening?
06:02Come back!
06:03Come back!
06:04The camera went with me.
06:06No, you see
06:06I obviously came down
06:08in the same place
06:09because although
06:09the Earth
06:10is moving at that speed
06:11we and everything
06:12around us
06:12is moving
06:13at the same speed
06:14even the air
06:15so we don't notice
06:16that we're moving
06:17at that speed.
06:18However,
06:19if the Earth
06:19ever stops spinning
06:20we'll all finish up
06:21in a big heap.
06:22So come on
06:23keep spinning!
06:25around and round
06:27and the Earth
06:28does keep spinning round.
06:31The question is
06:32why
06:33does it spin round
06:34as it does?
06:35Have you ever seen
06:49a teetotum?
06:51Well this is a model
06:51of one
06:52and if you spin it
06:53fast enough
06:53it should turn
06:55well
06:56all the children
06:57in the audience
06:57have got one
06:58see what happens
06:59when they spin them.
07:00Ready
07:00and
07:02spin!
07:03see what happens
07:09if you spin them properly
07:12they turn upside down
07:14now stop them for a moment
07:23and spin them again
07:25and this time
07:26notice the arrows
07:26on the side
07:27spin them
07:28in the direction
07:29of the arrows
07:30ready
07:31spin!
07:36now when they turn upside down
07:38notice which way
07:39the arrows are going
07:40as it slows down
07:42which way are they going?
07:49the other way
07:52now why
07:55should that happen?
07:57surely if you spin it
07:57that way
07:58when it turns upside down
08:00you'll be spinning that way
08:01well that
08:02isn't what happens
08:03what happens
08:04when you spin it
08:05is you set up
08:06an axis
08:07an imaginary line
08:08that runs straight
08:09down the middle
08:09and it's round that axis
08:11that the teetotum spins
08:12so that when it turns sideways
08:14it still spins
08:16round that axis
08:18and when it turns upside down
08:20it spins round that axis
08:21which means that the arrows
08:23are now going the other way
08:25try it again
08:27have another spin
08:28go!
08:29go!
08:29go!
08:29go!
08:30go!
08:30go!
08:31go!
08:32go!
08:33go!
08:34go!
08:35go!
08:36go!
08:37go!
08:38go!
08:39go!
08:40go!
08:41go!
08:42go!
08:43go!
08:44go!
08:45go!
08:46go!
08:47go!
08:47go!
08:47go!
08:47go!
08:47go!
08:48go!
08:48go!
08:49I've got this wheel
08:50spinning very fast
08:51round the axis
08:52which is the handles
08:53now
08:54I'm sitting on a revolving chair
08:56watch what happens
08:57when I move the axis
08:58I'm going round
09:03and now I'm coming back
09:06and I can
09:07set myself in one position
09:09now why
09:10is that happening
09:11I put my feet on the floor
09:13and put the axis there
09:15in another position
09:16now I'm not spinning
09:18well just slightly
09:19well just slightly
09:19now watch what happens
09:20when I move the axis
09:21I'm going round and round
09:28that's because the axis
09:31that is set up
09:32initially
09:33is the axis
09:36the spinning wheel
09:37wants to keep on
09:38so when I move it
09:41it's pulling
09:42to get back to its original position
09:43and that pull
09:45and that pull
09:45or push
09:46is enough
09:47to spin the chair round
09:49I've nearly run out now
09:51because it's going too slow
09:53there
09:54let's put the skids on this
09:56if anybody wants one wheel bike lessons afterwards
10:00come and see me
10:01that's what happens to the earth
10:03it spins round on its axis
10:05as that wheel did
10:06and it doesn't want to spin
10:07any other way
10:08but on that axis
10:09so it holds that axis
10:10and spins on it
10:11and spins on it
10:12and it's lucky for us
10:13that it does
10:14because it regulates
10:15the length of our days
10:17and as it spins round the sun
10:18the length of our years
10:20so much for roundabouts
10:22now what about
10:23the swings
10:23you'll wonder
10:28what swings
10:29have got to do with time
10:30well you'll see
10:31when you see
10:32our swingers
10:33come here
10:33the swingers
10:34you've got four swingers
10:37out you come
10:38that's it
10:41jump on your swings
10:42there we are
10:45you're all on
10:47your faces
10:48what are you doing
10:49oh
10:50come on I'll help you
10:51it's Tarzan
10:52you alright up there
10:55great
10:56have a swing
10:57and er
10:58see how you like it
11:00that's it
11:01I should hold you
11:02I'd hate you to be on the heap
11:03on the floor
11:04okay
11:04can we have some pushers now
11:06to help the swingers
11:07dangerous place to stand here
11:10isn't it
11:10can you come out
11:11and the swingers
11:12stop swinging
11:13and now we'll do it
11:15with the pushers
11:15what I want you to do
11:17is pull them all back
11:18so
11:19so they're all
11:20back at the same angle
11:21can you see
11:22there's one back to about here
11:24put one back a bit more
11:25and I'll say
11:26one two three go
11:27and let go
11:27ready
11:27one
11:28two
11:29three
11:29go
11:30let go
11:30and swingers
11:31don't swing
11:32hang absolutely
11:33like lead weights
11:34and see what happens
11:37you notice what happens
11:41this longer swing
11:42the one nearest the ground
11:44takes much longer
11:46to swing backwards and forwards
11:48whereas
11:49this one here
11:51is swinging
11:53much faster
11:54aren't you
11:55you alright
11:55up there
11:56like a budgie up there
11:58aren't you
11:58now these two
12:00are swinging about the same
12:01so this one
12:02one's getting ahead of the other
12:04so let's stop them
12:05and have a look at these two again
12:07all stopped
12:08right
12:09now we'll lift this one back
12:10just a little way
12:11but this one
12:13can you hold him there
12:13hold him there as well
12:14can you hold him
12:15and this one
12:16will pull back
12:17quite a long way
12:18ready
12:19and I'll say
12:20one two three go
12:21and we'll let go
12:21one two three go
12:23and see what happens
12:26now it's amazing
12:32because you're much bigger than her
12:34aren't you
12:34well you're older
12:35but the swings are the same length
12:38and although this one's swinging further back
12:40and further out
12:41they're taking the same time
12:45to complete a swing
12:46forwards and back
12:48and forwards and back
12:50and this one
12:51forwards and back
12:53the same time
12:55and that explains
12:58or helps to explain
12:59the principle of the pendulum
13:01with a pendulum
13:03it doesn't matter really
13:04what the weight is on the end
13:05it can be quite a big weight
13:06or a small weight
13:07it also doesn't matter
13:09how far out
13:11and back
13:11it swings
13:12the only thing
13:13that determines
13:14the number of times
13:15a pendulum swings
13:16is the length
13:17of the pendulum
13:18itself
13:19ok
13:20right
13:21off the swings
13:22thanks a lot
13:23can you go back to your seats now
13:24can I help you down
13:25jump
13:26oh
13:26I'm going to put the swings away
13:28thanks very much
13:29weren't they smashing
13:30long before the pendulum
13:38men used other methods
13:39of measuring time
13:40and the first method
13:41they ever used
13:42was the rays
13:44of the sun
13:45the sun
13:55as it shines
13:57casts shadows
13:58and the shadows
13:59move through the day
14:00and by plotting
14:02the movements
14:03of the shadows
14:04man could measure
14:05the hours
14:06but after the sun
14:11they used
14:11another method
14:13and that method
14:14was
14:15water
14:17water
14:17early water
14:38clocks
14:38were just
14:39an urn
14:40with water
14:41dripping into it
14:42but this
14:43is a model
14:44based on
14:45an 8th century
14:46Chinese water clock
14:48the water
14:54pours into these pans
14:55they get heavier
14:56until they overbalance
14:58and they knock down
15:02these levers
15:02which pull a chain
15:04which open
15:05a gate
15:07at the top
15:08and the gate
15:13allows one spoke
15:14to get past
15:16but catches
15:17the next spoke
15:18and so
15:22the wheel moves round
15:23one spoke at a time
15:25the original
15:30Chinese water clock
15:31was much bigger
15:32than this
15:33and in its day
15:35caused quite a splash
15:37but other methods
15:41of keeping time
15:42have been used
15:43through the centuries
15:43here are some of them
15:45this clock here
15:53dates back
15:54to
15:55round about
15:561350
15:57the original clock
15:58is still working today
15:59in a museum
16:00in Germany
16:01it's regulated
16:03by this gently
16:04swinging arm
16:05and that in turn
16:07can be speeded up
16:08or slowed down
16:09by the weights
16:10on the end of the arm
16:11being moved
16:12outwards
16:13or inwards
16:14this was made
16:17of iron
16:19later
16:21clocks were developed
16:22to be made of wood
16:23rather like
16:25this one here
16:26this clock here
16:31is different
16:32in that instead
16:34of the hands
16:34going round
16:35the face
16:36moves round
16:37slowly
16:42clocks were developed
16:43until this clock here
16:46which was
16:47the original
16:47was built in 1780
16:49and apart from just
16:50telling the hours
16:51and the minutes
16:52it also
16:53tells the
16:55phases of the moon
16:56and the tides
16:58it won't harm it
17:00if I move this round
17:01to show you
17:02that as it moves
17:03the tide at the top
17:05comes in
17:05and then goes out
17:08and all the time
17:15that's happening
17:16ticks away
17:17the hours
17:18and the minutes
17:19and those are regulated
17:21by the steady
17:23tick
17:24tock
17:25tick
17:26tock
17:27of the swinging
17:29pendulum
17:30in fact
17:35pendulums
17:36are so accurate
17:38they were used
17:38to record
17:39Greenwich Mean Time
17:40up until
17:411936
17:42but from then
17:44and especially
17:45quite recently
17:45the whole science
17:47of timekeeping
17:48has taken
17:49a dramatic
17:50turn
17:51what you are seeing
17:56now
17:56is light
17:58pulsing
17:59on and off
17:59a light
18:01beating
18:01on and off
18:02so you are seeing
18:02flashes
18:03of me
18:05and then darkness
18:06and my movements
18:08appear jerky
18:10switch it off
18:13my eyes are going funny
18:15anybody switching on
18:16at home
18:17they don't think
18:17they tell you
18:18it was on the blink
18:18don't they
18:18now
18:20those lights
18:21were going on
18:22and off
18:22very quickly
18:22pulsing
18:23but a pendulum
18:24pulses
18:25much slower
18:26now
18:29lots of other
18:30things pulse
18:31and surely
18:32the faster
18:33something pulses
18:33the less chance
18:34there is
18:35of a variation
18:36in its speed
18:37the less chance
18:38of error
18:38so the faster
18:39things pulse
18:40perhaps the more
18:41accurate they become
18:42after pendulums
18:44tuning forks
18:45were used
18:46a tuning fork
18:51always gives off
18:52the same note
18:53because
18:53the prongs
18:54of the tuning fork
18:55always vibrate
18:56at the same speed
18:57so tuning forks
18:58were used
18:59to regulate
19:00clocks
19:01and then
19:02someone discovered
19:03this
19:05it's called
19:11quartz
19:12and just a little
19:14chip
19:14of this stuff
19:15I've got a chip
19:18stuck on this
19:18card here
19:19just that little
19:20chip
19:20can be made
19:21to vibrate
19:22by just applying
19:23a very small
19:24electric charge
19:24but it vibrates
19:27incredibly quickly
19:28somewhere around
19:31two and a half
19:32million
19:32times
19:33a second
19:34and quartz
19:36clocks
19:37are very accurate
19:38and here's one
19:40that is extremely
19:43accurate
19:43in fact
19:47quartz digital clocks
19:48can be seen
19:49just about
19:51everywhere today
19:52however
19:56there's an element
19:57called cesium
19:58and someone discovered
19:59that just one atom
20:01of cesium
20:01can be made
20:02to vibrate
20:02not at two and a half
20:03million times a second
20:05but at nine
20:06thousand million
20:07times a second
20:08and now
20:10cesium atom clocks
20:11are used
20:12to regulate
20:12the world's time
20:13and the latest ones
20:15are so accurate
20:16the latest cesium
20:18atom clock
20:18it's estimated
20:20will lose
20:21just one second
20:22in the next
20:23three hundred
20:24thousand years
20:26although I don't know
20:28who's going to be around
20:29to check it
20:30time for a timely puzzle
20:33here I have
20:35a calendar
20:35full of dates
20:36not a calendar
20:37that's full of holes
20:38can I have a marker
20:39please
20:39oh you
20:40yes lovely
20:41if you take the pen
20:42now
20:43as you see
20:44I've already drawn
20:45a line there
20:46round
20:46nine numbers
20:49so if you
20:49can choose any month
20:51on the calendar
20:51and choose another
20:52nine numbers
20:53and draw a similar line
20:54and I'll get round here
20:55so I can't see what you're doing
20:56okay
20:57and as you do it
21:00can you stand to one side
21:01so that all your friends
21:02can see
21:03lovely
21:04okay
21:04now
21:05tell me the smallest number
21:07in that square
21:07five
21:09okay
21:10now what I want you to do now
21:11is choose any number
21:12any of the nine numbers
21:13and put a ring round it
21:14anyone you like
21:15okay
21:18now I want you to
21:19cross out
21:20all the numbers
21:21on the same row
21:22as it
21:23just the ones in the square
21:24and cross out
21:27all those
21:27above or below it
21:28now
21:34I'd like you to
21:35use one of the other numbers
21:36that hasn't been touched
21:37and put a ring round that
21:38right
21:41now cross out
21:42all those
21:42on the same row
21:43and all those
21:46above and below it
21:47and with luck
21:49you might have
21:50one number
21:51that's not touched
21:51right
21:52put a ring round that
21:53now if you add the three
21:56ring numbers up
21:57the answer will be
21:5939
22:00is that right
22:02amazing
22:04thanks very much
22:05for helping
22:06thank you
22:06that's lovely
22:07well
22:09if you'd like to know
22:11how that trick's done
22:12drop us a line
22:13because it's really simple
22:14you know
22:15once you know how
22:16so drop us a line
22:16Johnny Ball
22:17think of a number
22:18BBC Television
22:19London
22:19W12
22:208QT
22:21please include
22:22a stamped addressed envelope
22:23now
22:25time has caught up with us
22:26that's the end of the programme
22:27it's also the end of the series
22:28but we may be back
22:30in the future
22:30and who knows
22:32man in the future
22:34may learn to conquer
22:35time and space
22:37and travel faster
22:38and faster
22:39and faster
22:40you never know
22:41goodbye
22:42applause
22:44to the end of the programme
Recommended
24:16
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